There are previously known devices and methods for restoring electrical power to a load following a fault. In particular, U.S. Pat. No. 5,303,112 for FAULT DETECTION METHOD AND APPARATUS and U.S. Pat. No. 3,668,351 for SECTIONALIZING AND PROTECTIVE APPARATUS FOR SINGLE HOUSE TRANSFORMER describe typical electrical power distribution systems in which various customers and users (hereafter "loads") are supplied with electricity in networks such that power is distributed to the loads from more than one system network path or more than one source. In such distribution systems, faults may be isolated by employing sectionalizing switches while maintaining power delivery to the loads that are not in the immediate vicinity of the faulty sections, i.e., where the fault occurs. To achieve this fault isolation, various devices are arranged throughout the distribution system at appropriate locations to efficiently provide for the interruption and isolation of faults. These devices include fuses, circuit breakers, remote sectionalizing switches, and remotely and locally operated power distribution switches. Conventional power distribution systems commonly employ stand-alone, local logic and sensing devices for restoring power to loads following a fault.
For example, a conventional power distribution system receives at substations remotely produced high voltage through transmission lines. At a first substation, the high voltage is transformed by a transformer to a lower voltage for distribution through overhead or underground first feeder sections and associated transformers to a first set of loads. Likewise, a second substation produces a lower voltage for distribution through overhead or underground second feeder sections and associated transformers to a second set of loads. The first feeder sections are isolated from the second feeder sections by a remotely located, normally open ("NO") tie switch.
The first and second substations include associated first and second circuit breakers, which receive the lower voltage from the respective transformers and deliver the lower voltage through the respective feeder sections to the respective loads. Conventional circuit breakers include local controllers that sense a predetermined sequence of reclosing cycles in the presence of locally sensed overcurrents whereby delivery of electrical power is interrupted via the breaking of the circuit for predetermined intervals followed by the reclosing of the circuit. The reclosing sequence continues until either the fault is cleared or a predetermined number of reclosing operations have taken place, whereupon the circuit breaker locks out to continuously open the circuit until appropriate action can be taken by maintenance personnel to repair the circuit. In this manner, momentarily occurring overcurrents or fault conditions that are self-clearing allow the restoration and maintenance of power delivery to the loads without permanent opening or lock out of the circuit.
Remotely located along the first feeder sections between the first set of loads is a normally closed ("NC") sectionalizing switch, which is arranged to count the number of first circuit breaker reclosing operations. Likewise, remotely located along the second feeder sections between the second set of loads is another NC sectionalizing switch that is arranged to count the number of second circuit breaker reclosing operations. After a predetermined number of counts, for example, three, the relevant remote sectionalizing switch has sufficient local intelligence to open its switch during its associated circuit breaker open time period to isolate a particular fault and allow the circuit breaker to successfully reclose. At other locations, such as in branch sections of feeder lines, fuses may be provided and coordinated with the other protective devices to sense overcurrents and faults so as to interrupt current before the breakers, and/or sectionalizing switches can operate. Additionally, automated or manual distribution switches are provided at various points in the distribution network to provide suitable isolation, sectionalizing, and rerouting of power via different sources.
Information and control data regarding the operation, sensing, and control of the power distribution system is typically provided by a controller locally associated with each circuit breaker, sectionalizing switch, distribution switch, or circuit point. Data communication to system control processors in associated substations is typically via suitable communication channels, such as hardwires, radio, fiberoptics, telephone lines, or powerline carriers. The information and control data include the closed/lockout state of the breakers, closed/open state of the tie switch and sectionalizing switches, actuating command data for the above breakers and switches, and the sensed voltage and current at associated points in the power distribution system.
While particular breaker, switch, and parameter information is typically available throughout the power distribution system, presently available local control methods are not coordinated and can, therefore, erroneously respond to feeder faults as a result of magnetizing inrush currents, cold-load pickup, backfeed conditions, and overloads caused by corrective actions. Thus, in conventional systems, the location and cause of a feeder fault may not be confidently known via the information received at a control site.
What is needed, therefore, is an overall coordinated method of sensing and operating the various components in a power distribution system to efficiently locate, isolate, and restore the system after the occurrence of a feeder fault or overcurrent condition. In particular, what is needed is a feeder restoration method that provides faster power restoration to a greater number of loads than is provided by prior methods.